Planing Hulls with Twin Diesels...Economical?

[jm21]

So, I've been looking for boats...feeling like kind of a traitor for looking at powerboats but I'd like to live aboard and they just provide a lot more amenities. I don't really have enough money to support a total gas hog though. OTOH, I live a decent ways away from most places I'd like to go and being able to do 10-20 knots would greatly expand my weekend destinations.

I've seen a few boats on craigslist recently with twin 110-175 hp engines, from 28' to 40'. I'm just kind of curious as to how well these boats work. The diesels seem to be about half the HP of similar boats with gas engines yet they are claiming to have about the same cruising speeds.

Are they a lot more economical than their gas counterparts?

Some examples of ads for faster cruisers:

TWIN DIESEL 20 KNOT CRUISE LOW HOURS

32' Bayliner Conquest, 1984, Twin Volvo Diesel Engines! Meticulous!

And slower more trawler-like ones:

BAYLINER MOTORYACHT 40'

1986 Bayliner 3270 Twin Diesel

[cat man do]

Originally Posted by jm21

So, I've been looking for boats...feeling like kind of a traitor for looking at powerboats but I'd like to live aboard and they just provide a lot more amenities.

Go displacement, 50 foot trawlers with 100hp^v motors can get around 1 litre/NM doing 8 knots

[jm21]

My current budget is limited to about $40-50k max so 50' trawlers are basically out of the picture. And if I could afford a 50' trawler I'm guessing the expense of gas wouldn't be as big of a deal...

[cat man do]

Originally Posted by jm21

My current budget is limited to about $40-50k max so 50' trawlers are basically out of the picture. And if I could afford a 50' trawler I'm guessing the expense of gas wouldn't be as big of a deal...

A mate of mine had a 45 ft one of these that he got for $47k
This one uses 6 lph to do 8 knots
Cray Boat 40ft

Another mate of mine got one like this a few years back for around the same money as above without all the trawl gear on it TRAWLER 53 but in immaculate condition

A quick google shows this in the states 1979 Mainship 34'

[jm21]

Yeah, there are a few mainship 34's, some CHB 34's, a Hershine 37' in Nanaimo, and a few misc. somewhat custom trawlers in that price range.

I agree that bayliners are not exactly quality boats.

I know displacement hulls with appropriately sized engines are more efficient by a long shot.

Just curious mainly in how diesel planing boats compare to gasser planing boats. For example, in the case of the Bayliner Conquest, it has 2x165hp diesels and claims a cruising speed of 20 knots. The gasser versions seem to have 2x260hp gas engines and about 20-22 knots cruising. So, I'm wondering how much more efficient diesels would be. I imagine the gas engines on that boat get around 1.5mpg at cruise.

[GonzoF1]

Originally Posted by jm21

I agree that bayliners are not exactly quality boats.

The problem there is that this statement almost always comes from people that have never owned one.

(/I've never owned one)

Judge it on it's own merits. Not the word of others that may not have firsthand knowledge.

[David M]

Originally Posted by jm21

Yeah, there are a few mainship 34's, some CHB 34's, a Hershine 37' in Nanaimo, and a few misc. somewhat custom trawlers in that price range.

I agree that bayliners are not exactly quality boats.

I know displacement hulls with appropriately sized engines are more efficient by a long shot.

Just curious mainly in how diesel planing boats compare to gasser planing boats. For example, in the case of the Bayliner Conquest, it has 2x165hp diesels and claims a cruising speed of 20 knots. The gasser versions seem to have 2x260hp gas engines and about 20-22 knots cruising. So, I'm wondering how much more efficient diesels would be. I imagine the gas engines on that boat get around 1.5mpg at cruise.

For the same hull, a diesel is 30% more efficient minus the additional inefficiencie caused by diesels being heavier engines for a given horsepower. For a planing vessel, weight is a more critical factor than for a displacement vessel.

Your miles per gallon figure (or gallons per mile) is going to vary with the hulls displacement, hull shape and how fast you want to go which is a cubed relationship with maximum horsepower. To double the speed you pretty much must cube the horsepower.

You can look up an engines gallons per hour figure at a given horsepower or RPM by going to the engine manufacturers website.

[David M]

Diesel is definitely more efficient. You get roughly 30% more energy from a gallon of diesel. As for planing versus displacement, displacement is clearly more efficient by a huge margin.

Also, I would steer clear of Bayliners in general. There are many other better built used powerboats out there, especially in this economy. For planing powerboats, you may want to have a look at used SeaRays. Cummins and Caterpillars tend to be good diesel engines in that horsepower range. The newer John Deere's are also good. Avoid Volvo's...the parts extremely expensive.

[GonzoF1]

Yea... I've seen Carvers that made me scratch my head and ask the same question.

"So you have to go from the bow, run across the deck, up the stairs, down either the cockpit stairs or down the ladder, then open the surround glass to grab the stern line?... Ummm... Good luck with that on a rainy day Mrs. First Mate." :-)

[jm21]

Originally Posted by GonzoF1

Yea... I've seen Carvers that made me scratch my head and ask the same question.

"So you have to go from the bow, run across the deck, up the stairs, down either the cockpit stairs or down the ladder, then open the surround glass to grab the stern line?... Ummm... Good luck with that on a rainy day Mrs. First Mate." :-)

The carver aft cabins in particular seem like a disaster...but there must be some way...seems like you would have to run back out the stairs to the sundeck, grab the lines, then forward to the side decks, then a bounding leap off the high sides....

From what I'm reading it sounds like the higher repair and replacement costs for the diesels outweigh the fuel savings.

[David M]

Originally Posted by jm21

The carver aft cabins in particular seem like a disaster...but there must be some way...seems like you would have to run back out the stairs to the sundeck, grab the lines, then forward to the side decks, then a bounding leap off the high sides....

From what I'm reading it sounds like the higher repair and replacement costs for the diesels outweigh the fuel savings.

True, you have to burn a lot of diesel for them to pay for themselves. Gas engines are more economical for periodic use.

[RaySea Lady]

Originally Posted by jm21

From what I'm reading it sounds like the higher repair and replacement costs for the diesels outweigh the fuel savings.

My 450 cummins have 1300 hours on them and not much in repairs other than oil, filters and raw water impeller pumps every couple of years, and they are in great shape. Just had a cummins diesel tech go over them last month.

I don't know what repairs one could expect on gas engines with similar hours.

[RaySea Lady]

Originally Posted by GonzoF1

Yea... I've seen Carvers that made me scratch my head and ask the same question.

"So you have to go from the bow, run across the deck, up the stairs, down either the cockpit stairs or down the ladder, then open the surround glass to grab the stern line?... Ummm... Good luck with that on a rainy day Mrs. First Mate." :-)

Not sure what equipment the carver had, but on mine, I dock it alone and I also have to go to the upper deck and down to the cockpit.

But I have dual thrusters and I also have a mather portable helm that I take with me down to the bow and to the cockpit. It gives me full control of my engines and thrusters. So, with the right equipment, it is easy.

I would rather dock my twin engine 65 footer than a single engine 25 footer.

[boatpoker]

My Dave Martin designed "Trendsetter 40" with two heads, two staterooms, saloon, dinette and galley will cruise at 8 knots at 1.4 imp. gallons per hr. with a top speed of 20 knots at 4.5 gallons per hour with a single 235 Volvo TAMD 60B.
Power boats do not have to be fuel guzzlers !

[cat man do]

Originally Posted by boatpoker

My Dave Martin designed "Trendsetter 40" with two heads, two staterooms, saloon, dinette and galley will cruise at 8 knots at 1.4 imp. gallons per hr. with a top speed of 20 knots at 4.5 gallons per hour with a single 235 Volvo TAMD 60B.
Power boats do not have to be fuel guzzlers !

Never heard of them any more info?
Google wasn't my friend